This invention relates to parallel electric hybrid vehicles and combined series-parallel electric hybrid vehicles, and in particular to the location of the component parts.
There are basically four types of electric propulsion systems known for vehicles. First, there is a pure electric drive vehicle. The pure electric drive vehicle has an electric motor which receives power from a main battery pack via a controller. The controller controls the speed of the electric motor. The major disadvantage of a pure electric drive vehicle is that the range is very limited and the vehicle must be stopped and connected to an energy source such as an electrical outlet in order to be recharged.
The second type of electric propulsion system for vehicles is a series hybrid system. There are three major components in a series system: (1) a generator; (2) an electric motor arranged in series; and (3) an engine powering the generator. Mechanical energy generated by the engine is converted to electrical energy by the generator and is then converted back to mechanical energy by the electric motor. Each process of conversion is afflicted with losses and subsequent reductions of efficiency which is a significant disadvantage of this type of system.
The main advantage of the series hybrid is that it is possible to operate the engine at a fixed operating point within its engine speed/torque map. This point can be selected so that the engine functions with the greatest efficiency or produces particularly low emissions. Nevertheless, the efficiency of the entire series hybrid drive system is less than satisfactory.
The third type of electric propulsion systems is the parallel hybrid system, as described, for example, in U.S. Pat. No. 5,081,365. Parallel hybrid propulsion systems generally have three component areas: (1) electrical storage mechanism, such as storage batteries, ultracapacitors, or a combination thereof; (2) an electric drive motor, typically powered by the electrical storage mechanism and used to propel the wheels at least some of the time; and (3) an engine, such as a liquid fueled engine (e.g. internal combustion, stirling engine, or turbine engine) typically used to propel the vehicle directly and/or to recharge the electrical storage mechanism.
In parallel hybrid systems, the electric drive motor is alternatively driven by mechanically coupling it to the engine. When coupled, the engine propels the vehicle directly and the electric motor acts as a generator to maintain a desired charge level in the batteries or the ultracapacitor. While a parallel hybrid system achieves good fuel economy and performance, it must operate in an on and off engine parallel mode. In this mode, the stop-and-go urban driving uses electric power and the engine is used to supplement existing electric system capacity. For long trips, when the battery for the electric motor could be depleted, the vehicle cruises on the small engine and the electric system will provide the peaking power.
The primary advantage of the parallel hybrid drive over the series drive previously described is improved efficiency (lower fuel consumption) in the engine, since the engine's mechanical energy is passed directly on to the drive axle. The bulky generator is no longer required, thereby lowering both the cost and weight of the vehicle.
However, with extended stop and go urban driving, the battery pack will be often depleted and will need a charge in addition to the charge received from the electric motor. Or, the engine will be required to power the vehicle during the stop and go driving period thereby eliminating most beneficial effects of such an electric system. Therefore, the vehicle with a parallel system has limited inner city driving capabilities and range.
The fourth type of electric propulsion systems is the combined series-parallel hybrid system, as shown and described in application Ser. No. 07/880,967, the parent to the present application. The combined series-parallel system includes the advantages of both the series hybrid vehicle and the parallel hybrid vehicle. The combined series-parallel system also minimizes the disadvantages of both the series and parallel systems when taken separately. The series-parallel system is described more fully below.
The second, third and fourth systems described above have encountered space problems. The component parts were difficult to fit into a single vehicle, while allowing room for manufacture and subsequent maintenance work. For example, a typical parallel type of hybrid usually has a drive line, a drive clutch, a primary transmission, a mechanical clutch, an electric drive motor, a linkage to the secondary energy transfer clutch and from there a linkage to the internal combustion engine. The internal combustion engine and the electric motor have been squeezed into one end of the vehicle. Thus, hardware configurations have been fairly complex and bulky in the past. To provide additional space in some vehicles, manufacturers have reduced the size of the engines. This size reduction often accompanies a lower amount of power that the engine has to offer. The loss of power is counter productive to the industry's goal of increasing power in electric vehicles.